Periodic wave generator



July 22, 1941.

H. A. WHEELER PERIODIC WAVE GENERATOR Filed Feb. 13, 1939 2 shets-sheet 1 ATTORN EY July 22, 1941. l v H, A, WHEELER 2,250,170

PERIODIC WAVE GENERATOR Filed Feb. 13, 1939 2 Sheets-Sheet 2 Irr.

IMAGE FIGA: REPRoDucING g DEvIcE 2|/ Q SIGNAL sEPARAToR 51 D PRocEssog INVENTOR HAROLD A. WHEEL R ATTORN EY Patented July 22, 1941 UNITED vSTATES PATE NT OFFICE PERIODIC WAVE GENERATOR Harold A. Wheeler, Great Neck, N. Y., assigner to Hazeltlne Corporation, a corporation oi' Dela- Wale "4 A n Y 30 Claims.

This invention lrelates to periodic wave generators for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and relatively short retrace intervals.l While the invention is of general utility, it is of particular utility as a scanning-wave generator for a television signal receiver, especially as a line-frequency scanning generator.

For some purposes, it is necessary to pass through an inductance a current of saw-tooth wave form having relatively-long trace and relatively short retrace intervals. This requirement is found in modulated-carrier television signal receivers of the type which utilize a cathode-ray reproducing tube with magnetic scanning. Certain generators heretofore proposed for providing such a saw-tooth current have included an oscillator, the natural period of which is slightly greater than the period of the desired wave form, together with a source of synchronizing signals for synchronizingthe oscillator. The wave form during the trace interval of such oscillators generally depends on the time constant of an electrical circuit. Where such oscillators have been employed to deliver saw-tooth current directly to an inductive load, the appreciable resistance always present in such circuits has caused the rate of change of current to depart materially from uniformity which, during the trace intervals, is required for linearity of trace.

Various arrangements have been proposed to utilize an auxiliary tube coupled with the load inductance with a polarity opposite to that of the main tube of the oscillator to increase the approximation to linearity of the output-current wave during the trace interval. Certain of these arrangements comprise a diode coupled across the output inductance through which the linear saw-tooth current is required. These are called efliciency or damping diodes. depending on their function in the circuit with which they are coupled. The function of a damping diode is to provide damping of undesired transient oscillations during a portion of the cycle. The function of an eiiiciency diode is to increase the amplitude of the saw-tooth current without increasing the power consumption, but this improved eiiiciency is at the expense of linearity. While the resistance of the diode tends to stabilize the generated current wave form, it is incapable of correcting the defect of curvature and, in fact, lactually contributes to the curvature during the trace interval.

It is an object of the present invention, therefore, to provide an improved periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and relatively short retrace intervals.

It is a further object of the invention to provide an improved periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and relatively short retrace intervals, in which one or more of the above-mentioned disadvantages of the arrangements of the prior art are eliminated. l

. It is still another object of the invention to provide a periodic wave generator for supplying to an inductive load circuit a current of sawtooth wave form having relatively long trace and relatively short retrace intervals, in which the voltage across the load circuit is independently regulated during the tra-ce intervals in such a manner that the rate of change of saw-tooth current in the load circuit is substantially uniform and the wave form is substantially linear during the trace intervals.

In accordance with the invention, a periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprises, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes eectively coupled across the load circuit with a givenv polarity, and a low-mu vacuum tube having output electrodes effectively coupled across the load circuit with opposite polarity. 'The generator includes means for controlling' the high-mu tube.

to cause its output current to vary in one sense during trace intervals and means for controlling the low-mu tube to cause its output current to vary in the opposite sense during trace intervals. The relative controls of the two tubes are so proportioned that the saw-tooth current in v the load circuit has a predetermined variation with time during trace intervals.

In a preferred embodiment of the invention, the low-mu vacuum tube comprises a control `electrode to which is applied a saw-tooth voltage derived from the load circuit of the generator, preferably from a series-connected resistor and condenser coupled across the load .circuit. Also, in a preferred self-oscillating embodiment of the invention, the means for causing 'the output current of the screen-grid tube to increase during trace intervals comprises a regenerative feed-back circuit from the output of each trace interval.

Also in accordance with the invention, a pean intermediate-frequency amplifier I4, a detector I5, a video-frequency amplifier I6, and

riodic wave generator for supplying to an inf ductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprises, a load circuit constituting primarily inductance, a first vacuum tube having output electrodes effectively coupled across the load circuit with a given polarity, and a second vacuum tube having anode and cathode output electrodes effectively coupled across the load circuit with opposite polarity, the second vacuum tube having a control electrode. The generator includes means for controlling the first tube to cause its output current "to increase during the trace intervals while a coupling path is provided from the anode to the control electrode of said second tube for maintaining the eifective anode-cathode resistance of 4the second tube less than its actual anode-cathode resistance during the trace intervals. The

coupling path includes means for applying to the control electrode a saw-tooth voltage of such polarity as to cause the output current of the second tube tol decrease during the trace intervals.

Also in accordance with the invention, there is provided a periodic wave repeater for supplying to an inductive load circuit a current of sawtooth wave form having relatively long trace and short retrace intervals comprising, two vacuum tubes, each having a cathode, an anode, and a control electrode. A space current supply circuit is provided for the tubes, the supply circuit whereby the other of the tubes is caused to present in series with the first tube an eective anode-cathode resistance less than' its actual anodecathode resistance.

For a `better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out vin the appended claims. L

In the drawings, Fig. 1 is a circuit diagram, partly schematic, of a complete modulated-carrier television signal receiver embodying one form of the invention as the line-frequency scanning generator; Figs. 211,212, 2c, 2d, 2e, 2f, and Fig. 3 are graphs illustrating certain of the operating .characteristics of the circuit of Fig. 1; while Figs. 4 and 5 illustrate other embodiments of the invention suitable for-use as high-frequency oscillators.

lReferring now more particularly to the drawings, the system illustrated in Fig. 1 comprises a modulated-carrier television signal receiver of the superheterodyne type including an antenna system I0, II connected to a radio-frequency amplier I2 to which are connected in cascade, in the order named, an oscillator-modulator I3,

an image-reproducing device Il. A line-irequency generator I8 and a field-frequency generator I9 are coupled to the output circuit of the detector I5 through a synchronizing-signal separator and processor 20, the line-frequency generator I8 being coupled to a line-scanning winding 2| of image-reproducing device I1, in a manner to be hereinafter fully described, and the output of the field-frequency generator I9 being coupled to a field-scanning winding of imagereproducing device I1 in a conventional manner.

The stages or units Ill-Il, inclusive, I9,A and 20 may all be of conventional well-known construction so that detailed illustration and description thereof are unnecessary herein.

Referring briefly, however, to the operation of the above-described system as a whole, television signals intercepted by antenna circuit I0, II are selected and amplified in radio-frequency amplifier I2 and coupled to the oscillator-modulator I3, wherein they are converted into intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier I4 and delivered to detector I5. The modulation components of the signals are derived by the detector I5 and are supplied to the video-frequency amplifier I6, wherein they are amplified and from which they are supplied in the usual manner to a brightness-control electrode of the image-reproducing device I'I. The modulation components are also supplied to the synchronizing-control circuits of generators I8 and I9. The intensity of the scanning beam of the device I'I is modulated or controlled in accordance with the video-frequency voltages impressed upon its 'brightness-control electrode in the usual manner. Scanning waves are generated in the line-frequency and field-frequency generators I8 and I9, respectively, which are synchronized by the output of synchronizing-signal separator and processor 20 and applied tothe scanning elements of the image-reproducing device to produce electric scanning elds, thereby to deflect the scanning wave in two directions normal to eachother so as to trace a rectilinear pattern'on the screen and thereby to reconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1 embodying the present invention, there is provided an eiiicient sawtooth current generator I8 for generating a periodic wave having relatively long linear trace and short retrace intervals, the use of which provides all the advantages which might be obtained by both an eiiiciency diode and a damping diode, and the additional advantage of correction for curvature of the output wave form during the trace interval. In order to procure these desirable results, an amplifier tube is utilized in place of the eiciency or damping diode. In order to retain the advantages of the low resistance of the diode, an amplifier tube of very low resistance is chosen. Such low resistance is compatible with an amplifier tube having a small amplification factor or mu, preferably less than unity, or at least between the limits of f3 and 3, which may be obtained with a triode so connected that its control electrode and anode elements -are interchanged with respect to their usual functions. Connected in this way, a triode normally having an amplification factor of 3 and an anode resistance of 2,100 ohms becomes a triode with an amplification factor of 1/3 and a lcircuit of tube 3|.

amplifier tube having a very large amplification factor, preferably or'greater, or between the limits of 10 and 1,000, the high-mu tube preferably being of the screen-grid pentode type or the beam-tetrode type, the two tubes together 'bef having somewhat like a push-pull amplifier or oscillator.`

Fig. l'shows such a combination together with an additional tube utilized as a driver for detube 3| and a second or low-mu reversed-triode tube 32, the tubes 3| and 32 having output circuits including electrodes and 23, respectively,

coupled with oppositepolarity to the'load, circuit of the system which constitutes primarily inductance. Tube is coupled to unit 2|) to derive therefrom synchronizing pulsesl and repeat them as currentpulses occurring only dur, ing the retrace intervals, the tube 30 being cut oi! during the trace intervals. In order to develop an inputl voltage of the required wave form for the control electrode 26 of tube 3|, there is provided a wave-shaping-circuit comprising a series-connected resistor 33 and condenser 34 connected across the output circuit of tube 30. Condenser 34 is shunted by a resistor 35 to carry the unidirectional component of the space current of tube 30; that is, to discharge the condenser 34 slowly during the trace intervals, thereby to produce a saw-tooth voltage component. The resultant of this saw-tooth voltage and the negative-pulse voltage drop across resistor 33 is applied to the input electrodes of tube 3| by means of a coupling condenser 36 and grid-leak resistor 31 to cause the output current oi' the tube tol vary in one sense, specifically, to increase, during trace intervals.

Tube 3| is a high-mu tube and preferably includes some means for suppressing secondary emission from its anode, a beam-type tube being assumed for this purpose in Fig. 1. The output circuit of tube 3| includes a parallel resonant circuit comprising shunt capacitance 38, shown in dotted lines for the reason that it may be comprised in Whole, or in part, of the inherent capacitance of the circuit, and the load in' ductance of scanning coil 2|. In the circuit of Fig. 1, scanning coil 2| is coupled into the tuned circuit by meansl of anv impedance transformer comprising inductiveiy coupled primary and secondary windings 39, 40, respectively, for converting the small inductance of scanning coil 2| to the larger inductance required in the outputl The effective inductance of the resonant output circuit of tube 3| is thus that of the transformer primary winding 39 as measured with the scanning coil 2| connected` across the secondary winding 40.

Tube 32 is associated only with the resonant load circuit and is essentially a stabilizing device which is designed to act as a negative resistance device during the trace interval, increasing the amplitude of the current in/the load circuit and compensating, at least partially. for

the resistance therein. It has no effect during the retrace interval and particularly'd'oes not obstruct the occurrence of a half vcycle of free oscillation in the load circuit during the retrace interval. The electrode 22 of tube 32, usually used as the anode, is here used as a control elecof the circuit of Fig. 1.

trode and is more remote from lthe cathode 23 than is the electrode 23 here used as the anode. The electrode 22 is subjected toa variable negative voltage which controls a relatively large amount of current in the output circuit of tube 32, which is here the circuit comprising grid 23 and cathode 23. Voltage variations in the output circuit of the tube 32 are, therefore, less than variations of the control voltage applied to its input or control circuit, but the variations of output current are relatively large, while substantially no current is required in its input circuit. .The reversed triode 32, therefore, is still an eiiicient power amplifier, even though it is not a voltage amplifier. t Such an arrangement has been called a voltage-reducing amplifier. Its properties are adapted for use in the circuit of Fig. l primarily because, during the trace interval, a large current swing is required in the load circuit with only a small change of anode voltage. Also, the relatively large saw-tooth control voltage required in the input circuit of tube'32, as so connected, may be obtained from the load circuit of the system by virtue of Vthe high peak voltage which exists across the load circuit during the retrace interval, as will be explained hereinafter. This saw-tooth control voltage is obtained across a condenser 4| connected in series with a resistor 42 directly across the load circuit. The voltage across condenser 4| is coupled to the control electrode 22 of tube 32 through a coupling condenser 43 and a leak resistor 44 to cause the output current of the tube to vary in a sense opposite to the current variation of tube 3|, speciiically, to decrease, during the trace intervals. The relative amplitudes and polarities of the control voltages of the tubes 3| and -32 are so proportioned that th'e sawtooth current in the load circuit 40, 2| has a predetermined variation with time during trace intervals, and preferably so that the rate of change o f current is maintained uniform during the trace intervals. An adjustable resistor 45` may, in certain cases, be included in series with inductance 2| across the secondary circuit 4|! of the load circuit to compensate for residual curvature, as explained hereinafter. Suitable unidirectional sources of voltage are supplied for tubes 30, 3|, and 32, as indicated in the draw-v ings.

Reference is made to Figs. 2a2f, inclusive, and Fig. 3 for an explanation of the operation Fig. 2a illustrates the wave form ofthe desired saw-tooth current in scanning coil inductance 2|. This current flows through the inherent resistance of coil 2| and through resistor 45, if included. The saw-tooth wave form of Fig. 2a is linear over the trace intervals and' comprises a half-sine wave during each retrace interval. 'I'he shape of the wave during the retrace interval is immaterial as far as scanning is concerned, the half-sine wave being the normal shape of the free oscillation of the output circuit during the retrace interval.

Assuming that a saw-tooth current having the wave form of Fig. 2a flows through the scanning inductance 2|, Fig. 2b illustrates the wave form of the voltage at the anode of tube 3|, While lthe average anode potential of tube 3| is represented by the dotted line Eb. The pulses of high amplitude in the full-line curve are`caused by w the rapid decay of current in the load inductance 2| during retrace intervals when both tubes` 3| and 32 are nonconductive.- The slight slope during the trace intervals represents the .voltage drop of tle saw-tooth currentv in the resistance of the load circuit. Therefore, if a voltage of this waver form is developed in the anode circuit of tube 3|, it followsthat the current in are reduced to zero during the retrace intervals.

The required energy is supplied to the load circuit only during the trace intervals, one-half cycle of free oscillation taking place in the load circuit during each retrace interval.

In Fig. 2c is illustrated thewave form of the lanode current required to be developed by tube,

3|, while in Fig. 2d there is illustrated the wave form of the current required to be supplied .by the tube 32. It is seen that the current increases during the trace interval in the high-mu tube 3| and decreases during the trace interval in the low-mu tube 32. n

In order to explain a complete cycle of operation of the periodic wave generator just described, it is assumed that the anode current of tube 3| has reached its maximum value and that the output current of tube 32 is zero. This condition is shown at point t1 in Figs. 2c and 2d. `Atthis instant it is necessary to apply a posiytive pulse to the grid of tube 30 froml synchronizing-signal separator and l processor 20. This positive pulse generates a negative pulse across -resistor 33 which is applied to tube 3| suddenly to swing the control grid thereof negative beyond its cutoff point. Load inductance 2| at this instant is carrying maximum current which is thereby diverted to ow through capacitance 38 because that is the only remaining current path, the high-mu tube 3| being biased beyond cutoif and the low-mu tube 32 being swung be- `vond its cutoff point as the terminal of capacitance 38 connected to the cathode 29 of tube 32 is charged highly positive. The decay of current in inductance 2| is accompanied by an `increase in the charge on capacitance 38 until the current in inductance 2| reaches Zero, at which time the voltage across condenser 38 reaches its maximum value. The condenser then dischargesy through the inductance 2| and through transformer 39, 40, gradually building up the reverse current in inductance 2| to a value nearly equal to its previous maximum` value. This process completes a half cycle of free oscillation during the retrace interval.

As the voltage across the load circuit falls at the end of the retrace interval, the cathode potential of low-mu tube 32 also falls and it becomes suddenly conductive to carry the reverse current of load inductance 2| and thereby to prevent a further decrease in voltage across the load circuit by reverse chargingjof the capacitance 38. The output current of tube 32 immediately assumes its maximum value at the end of the retrace interval and at the same time the pulse from the tube 30, which loperated the high-mu tube 3| beyond its cutoff point, is discontinued. The current then gradually rises in tube 3| during the succeeding trace interval, the rate of change of current in its output circuit being determined entirely by the wave form of the voltage on lts control electrode and at the same time the current gradually fallsv in tube 32,

due partly to variation of the voltage between its output electrodes and partly to the .wave form of the negative voltage on its control electrode 22. There remains only theproblem of properly proportioning the voltages on the input electrodes of tubes 3| and 32 to procure this desirable result.

Due to the factA 'that tube 3| is a screen-grid or beam-tetrode tube, the anode voltage has no appreciable effect on its anode current. Therefore, the rising vcurrent characteristic of Fig. 2c during the trace interval must be caused entirely by decreasing negative voltage on its input electrodes. The full-line curve of Fig. 2e illustrates the wave form of the required grid voltage. This wave Aform has negative pulses which operate tube 3| beyond its cutoff point during retrace intervals and has saw-tooth components during trace intervals. This input voltage for tube l3| is derived from resistor 33 and condenser 34 in the anode circuit of tube 30. The resistor 33 and condenser 34 are so proportioned that the saw-tooth voltage component derived by tube 30 from the synchronizing-signal pulses applied thereto, during the trace interval, is of such value that tube 3| is operated near its cutoff point at the beginning of the trace interval and so that its output current increases steadily as the grid-bias voltage approaches zero at the end of the trace interval.

Normal operation of tube 3| is preferably without any gridcurrent, although a small amount of grid current is not necessarily detrimental in the operation. To this end tube 3| is supplied with a grid-bias voltage, as represented by the dotted linelEc of Fig. 2e. In some cases the source of grid bias for tube 3| may be omitted if the small grid current through grid leak 31 is sufcient to furnish the necessary grid bias.

The output current of tube 32 depends. both on the voltage of -the load circuit of the system, represented by the full-line curve of Fig. 2b, and on the control voltage applied to the control electrode 22 of the tube. Fig. 2J illustrates the -various voltage wave forms associated with tube 32. Curve m, which is the same as the curve of Fig. 2b, represents the voltage of the cathode 29 of tube 32 with respect to ground. The circuit of output electrode 23 of the tube includes a source of negative-bias voltage which, together with the anode source of tube 3|, gives it a steady bias with respect to ground, as shown by line Ed. Line n represents the bias voltage of the control electrode 22 of tube 32, while curve o represents its alternating voltage. It is noted thatl .the output voltage of tube 32, comprising the difference between curves m and Ed increases slightly during the trace interval. This tends to increase the output current of tube 32, Whereas decreasing current is desired to augment the current in the load circuit. The decreasing output current of tube 32 is, therefore, obtained as desired by providing on the control electrode 22 of the tube a saw-tooth control voltage which becomes increasingly negative during the trace interval and is nearly suflcient to cut off the tube at the end of the trace. interval. Such a sawtooth voltage is obtained across condenser 4| which integrates the impulse component of the voltage across the load circuit.

'I'he co-operation' of the output currents of rtubes 31 and 32 in providing the desired saw- 2,250,170 the high-mu tube 3| is shown in the upper part of the diagram. while .that ofthe low-mu tube 32 is shown vin the lower part of the diagram'. The currents are plotted in opposite directions because they flow in opposite directions through the load circuit. Each set of curves is plotted for fixed control-bias voltages progressively increasing negatively from zero. The curves are shown ideally as straight lines to emphasize the low resistance of the low-mu tube 32, as compared with the high resistance of high-mu tube 3|. The closed curve r represents the currentvoltage locus of load inductance 2| over an operating cycle of the system, the arrow showing the direction in which this locus is traced. This locus is obtained by plotting the current of Fig. 2a against the voltage of Fig. 2b. During a trace interval the voltage varies so slowly that the current through capacitance 38 is negligible. During a retrace interval fthe-tubes 3| and 32 are both operated beyond their cutoi points so that the current of the load circuit all flows entirelythrough the 'capacitance 38, the shunt path including resistor 42 and condenser 4| being of vsuch high impedance as to carry a negligible current. At the endv of the retrace interval, curve r intersects the zero-bias 1 curve of triode 32 where the output current of tube 32 vreaches its maximum value. The output current of tube, 32 then decays during the succeeding trace interval at the same time that the output current of tube 3| is building up to its maximum value. The decay of current in tube 32 and the rise of current in tube 3| are represented by dotted lines s and t, respectively. The total current of the load circuit during the trace interval is the difference between the values of curves s and t and is represented by full line u.

It will be understoodv that the generator I8 of Fig. 1 Iis essentially an amplifier which is driven by the positive synchronizing pulses applied from unit 23. Due to the feed-back voltage applied to tube 3 2, the tube behaves as a negative resistance during the trace interval. This "characteristic is illustrated by the reverse slope of curve s relative to the characteristic curves of tube 32 which appear in the lower part of Fig. 3. This negative resistance characteristic is obtained by simultaneous variation ofthe control-electrode and output-electrode voltages in opposite senses relative to the cathode of the tube. This negative resistance is an essential factor in causing cancellation of curvature of the saw-tooth current wave form during trace intervals, which otherwise would be caused by series resistance in the load circuit of the system, while also increasing the amplitude of the sawtoo'th output current. Low-mu vacuum tube 32 essentially has an internal resistance between its output electrodes which is substantially less than the impedance of the load circuit of the system at the frequency of the saw-tooth wave. Preferably, the time constant of the circuit comprising the inductance of the load circuit and the internal resistance between the output electrodes of tube 32 duringthe trace intervals is of the same order of magnitude as, or greater than, the

period of the trace intervals of the system. In a preferred embodiment of the invention, such time constant is approximately equal to. or greater than, the period of the trace intervals of the system; or in another embodiment, within the limits of 1;/3 and 3 times the trace period.

In the operationv of the circuit of Fig. l, it is seen that the saw-tooth voltage developed across condenser 4| is not applied directly between the cathode 29 and control electrode 22 but rather is applied between the anode 23 and control electrode 22. Therefore, there is impressed between the cathode 29 and control electrode 22 not only the saw-tooth feed-back voltage developed across condenser 4|, but also any voltage fluctuations which are present in the load circuit 39 or, in other words, which are present in the common anode-cathode circuit of tubes 3| and 32. These voltage fluctuations are coupled with the same polarity from the anode-cathode circuit to the control electrode-cathode circuit of tube 32 so that this feedback is degenerative and acts to decrease the enea-tive anode-cathode resistance of tube 32 to a value less than its actual anodecathode resistance in a manner well understood in the art. It is also seen that the two vacuum tubes 3|, 32 have their anode-cathode circuits connected in series in a closed direct current operation.

path including the unidirectional supply sources of the tubes.

It may be convenient, in practice to reverse the curvature which would be caused by the resistance of the load cincuit, by applying. more saw-tooth voltage to the control electrode of tube 32 than is actually required, and then to adjust the value of resistor 45 to secure exact cancellation of the curvature in the output Wave form during the trace interval. Such an adjustment is convenient because it modifies the curvature without noticeably affecting the amplitude of the saw-tooth current output. Adjustment for curvature in this manner is a subject of applicants copending application, Serial No. 253,034, filed January 27, 1939.`

Ina-smuch as the generator I8 of Fig. l is driven, driving or synchronizing pulses of fairly high amplitude are required during the entire retrace intervals of the system. In Fig. 4 there is illustrated a modification of the circuit of Fig. 1 comprising a feed-back circuit so that the generator is essentially an oscillator which can be synchronized with a relatively weak pulse of short duration at the beginning of the retrace period. This is the conventional method of ysynchronizing and it will be understood that in this embodiment the usual line-frequency pulses are derived from unit 20. Similar circuit elements have identical reference numerals in the two iigures. The feed-back circuit of Fig. 4 comprises acondenser 50 coupled between the anode,25 of tube3| and the control electrode of tube 30, a coupling condenser 5I being included in the input circuit of tube 30. Capacitance 53 represents the inherent capacitance of the input circuit of tube 3| eiectively in parallel with condenser 5| and providing, with condenser 5|), a voltage divider across the output circuit of tube 3|. The input circuit of tube 30 may be provided with a grid leak 54.

A capacitance current flows from the anode -circuit of tube 3| through condensers 50 and 5| to the synchronizing input circuit, which may cause interference with the normal synchronizing Therefore, this feedback into the synchronizing circuit is preferably neutralized by means of a condenser 52 coupled between the anode of tube 30 and one terminal of condenser 5|. Neutralization is provided, due to the fact that the retrace pulse voltages on the anodes of the tubes 30 and 3| are of I'he following equation gives the relation between opposite polarity.`

-the trace interval.

where each of the subscripts indicates the particular circuit element of Fig- 4 with which each capacitance C is associated, and E1 and Ez are the pulse voltages on the anodes of tubes 30 and 3|, respectively. This neutralization circuit is not effective during the trace period, when it is less needed, because the capacitive currents are then very small.

The operation of Fig. 4 is essentially identical to that of Fig. 1. The free oscillation period of the oscillator in the absence of synchronizing pulses is made slightly longer than the period of the synchronizing pulses. The effect of each positive synchronizing pulse is then to start a cur-` rent pulse in tube 30, thereby to interrupt the trace interval just before it would naturally be concluded and initiate the retrace interval. Grid leak 54 of tube 30 of Fig. 4 may be proportioned to make the tube increasingly susceptible to a synchronizing pulse toward the end of the trace interval. This is advantageous because it requires less coupling from the synchronizing circuit and thereby decreases the sensitivity-to-noise interference which might interrupt the normal operation of the system. The feed-back circuit normal- 1y impresses on the input electrode of tube 30' a strong short positive pulse during the retrace interval and a weak long negative pulse during Resistor 54 may thus be proportioned to discharge part of the weak negative pulse during the trace interval so that the grid ybias of tube 30 is gradually reduced during the trace interval and a synchronizing pulse of only a small amplitude is necessary at the end of the trace to actuate tube 30.

Another modification of the invention is illustrated in Fig. 5. Circuit elements which are similar to those of previous figures have identical reference numerals. Fig. 5 comprises an autotransformer 39', 40' and a feed-back transformer replaces the function of tube 30 of Fig. 4. A bias voltage is provided for tube 3| by means of a cathode resistor 60 by-passed by a condenser 6|. The bias voltage for the control electrode 22 of tube 32 in the embodiment of Fig. 5 is provided by resistors 63 and 64 coupled in series between anode 23 and ground. The anode 23 receives a steady bias across a resistor 62, bypassed by a condenser 65, this resistor preferably being adjustable. Tube 32 comprises a filament 29 heated by a separate winding on a power sup-A ply transformer, this coil being designed to have minimum capacitance to other parts of the trans-` denser 14 complete a neutralizing circuit. Capacitance 15 representsthe inherent grid-cathode capacitance of tube 3| and its associated circuit.

In considering the operation of the circuit of Fig. 5, it will be seen that there are three components of voltage effectively in series in the input circuit ofv tube. 3|, namely, 4the synchronizing pulses from the source 20, a saw-tooth component derived across condenser 68, and the transformer voltage of Winding 61 which supplies mainly a strong negative pulse during the retrace interval. The conditions for neutralization are: ELS/Lil N.. C1. R10 (2) where N, C, and R represent. respectively, the number of turns, capacitance, and resistance,

and the subscripts identify the circuit elements R12 Cos (3) Resistor 12 also serves as a grid leak for tube 3|. f The following circuit constants are given as i1-` lustrative of values of circuit elements which may be utilized in the circuit of Fig. 5:

Tube 31 Type 42 Tube 32 Type '11A Resistor 42 1 megohm Resistor 45 0 to k10v ohms Resistor 60 700 ohms Resistor 62 9,000 ohms Resistor 63 10 megohms Resistor 64 10 megohms Resistor '10 5,000 ohms Resistor '71 15,000 ohms Resistor 72 1 megohm Resistor 73 0.1 megohm Capacitance 38 Aboutf100 puff.

' Capacitance 41----' 100 auf.

Capacitance 43 0.001 tf. Capacitance 61 1 pf. Capacitance .65 1 af.

Capacitance 68 800 paf. Capacitance 69 500 upf. Capacitance '74 20 auf.

former so that it does not'l add appreciable capacitanceacross the load circuit.

'Ihe inductive feed-back circuit of the oscillator of Fig. 5 is designedto supply to the input electrode of tube 3| the wave form of Fig. 2e and at the same time to neutralize the interfering feedback into the source of synchronizing signals y 20 from which the required negative synchronizing pulses are derived. This feed-back and neutralizing circuit includes windings 66 and 61 Capacitance 'I5 (partly in transformer) 60mm Source of operating voltage for tubes 31 and 32 .300 volts Winding 39'.. 420 turns Winding 40' '10 turns Winding 66 210 turns Winding 6'7 '10 turns Inductance 21 2 mh. Line frequency 13,230 cycles Retrace factor retrace time 0.12

on the output transformer of the oscillator, the

source of synchronizing signals 20, condensers 68 and 69, winding 61, and resistor 10 all being connected in series in the input circuit -of tube 3|. Winding 66, resistor 13, and condenser 68 are provided to generate a saw-tooth feed-back voltage across condenser 68, in the input circuit of tube 3|. while resistors 10, 1| and 12 and conline period Pulses from source 20 having magnitude of 5 to l0 volts negative.

While the invention has beenl illustrated asapplied only in the. line-frequency channel, it will be understood that the circuit of field-frequency generator |9 may also incorporate a circuit in accordance with the invention.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to lcover all such changes and modications as fall within the true spirit and scope of the invention.

What is claimed is: 1. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a highmu vacuum tube having output electrodes eftecrelative controls of said two tubes being so proportioned that said saw-tooth current in said load circuit has a predetermined variation with time during said trace intervals.

2. A periodic Wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a highmu vacuum tube having output electrodes effectively coupled 4across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled acrosssaid load circuit with opposite polarity, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, the relative controls of said two tubes being so proportioned that said saw-tooth current in said load circuit has a predetermined variation with time during said trace intervals.

3. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a highmu vacuum tube having output electrodes eiectively coupled across said load circuitwith a given polarity, a low-mu vacuum tube having output electrodes eiectively coupled across said load circuit with opposite polarity, the mu of said high-mu vacuum tube being greater than and that of said low-mu tube being less than 3, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and means for controlling said low-mu trodes eectively coupled across said load circuit withopposite polarity, the mu or said high-mu vacuum tube being between the limits of l0 andv 1000 and that of said low-mu tube being between the limits of V3 and 3, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease .during said trace intervals, the relative controls of said 'two tubes being so proportioned that said saw-tooth current in said load circuit has apredetermined variation with time during said trace intervals.

5. A periodic wave generator-for supplying to en inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance,v a. high-mu vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupledacross said load circuit with opposite polarity, means for controlling said high-mu tubeto cause its output current to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two control means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said saw-tooth current in said load circuitis maintained substantially'uniform during said trace intervals.

6. A periodic wave generator for supplying to an inductive load circuit of a given impedance at the wave frequency a current of saw-tooth Wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said load circuit with opposite polarity, said low-mu vacuum tube tube to cause its output current to decrease during said trace intervals, the relative controls of said two tubes being so proportionedthat said saw-tooth current in said load circuit has a predetermined variation with time during said trace s intervals. I

having during said trace intervals internal resistance between its output electrodes much less than said impedance of said load circuit, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and means for controlling saidr low-mu tube to cause its voutputcurrent to decrease during said trace intervals, said two control means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said sawtooth current in said load circuit is maintained substantially uniform during said trace intervals.

7. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals, comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said load circuit with opposite polarity, the time constant of the circuit comprising the inductance of said `load circuit and the interval resistance of said low-'mu vacuum tube during said trace intervals ,having at least as great an order of magnitude as the period of said trace intervals. means for to cause its output current to decrease during said trace intervals, said two control means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said sawtooth current in said load circuit is maintained substantially uniform during said trace intervals.

8. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes eiectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes electivel'y coupled across said load circuit with opposite polarity, the time constant of the circuit comprising the inductance of said load circuit and the internal resistance of said lowmu vacuum tube during said trace intervals being greater than 1/3 and less than 3 times the period of said trace intervals, means for controlling said `highmu tube to cause its output current to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals,

`said two control means being proportioned tov to an inductive load circuit a current of sawtooth wave form having relatively long linear trace and short retrace intervals comprising, a

low-mu tube to decrease during said trace in- 9. A periodic wavef generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retraceiintervals comprising, a load circuit constituting'primarily inductance. a'first vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a second'vacuum tube having anode and cathode output electrodes effectively coupled across said load circuit with opposite polarityl and having a control electrode, means for controlling said first tube ,to cause its output current to increase during lsaid trace intervals, a coupling path from said anode to said control electrode for maintaining the eiective anode-cathode .resistance of said second tube less than its actual anode-cathode resistance during said trace intervals, vand means included in said coupling path for applying to said control electrode a sawtooth voltage of such polarity as to cause the output current of said second tube to decrease` tervals and of such magnitude that the rate of change of said saw-tooth current in said load circuit is heldv substantially uniform during said trace intervals.

12..A periodic wave generator for .supplying to an inductive load circuit a current of sawtooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a first vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a second vacuum tube having anode and cathode output electrodes eiectively coupled across said load circuit ,with opposite polarity and having a control electrode, means for controlling said iirst tube to cause its output current to increase during said trace intervals, a coupling path from said anode to YV'said control electrode for maintaining the effective anodecathode resistance of said second tube less than its actual anode-cathode resistance during said trace intervals, and means included in said coupling path for applying between said anode and saidv control electrode a saw-tooth voltage of such y polarity as to cause the output current of said second tube to decrease during said trace intervals and of such magnitude that the rate of change of said saw-tooth current in said load circuit is maintained substantially uniform.

given polarity, a Alow--mu vacuum tube having output electrodes eilectively coupled across said load circuit with oppositepolarity and/having a control electrode, means for controlling said high# mu tube to cause its output current to increase during said trace intervals, and means for applying to said control electrode a saw-tooth voltage of .such polarity as to cause the output current of said low-mu tube to decrease during said`trace intervals and of such magnitude that the rate of change of said saw-tooth current in said load circuit is maintained substantially uniform during said trace intervals. i

11. A periodicwave generator for supplying 13. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes eiectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said Vload circuit with opposite polarity, means for applying to said input electrodes a saw-tooth voltage of such polarity as to cause the output current of said high-mu tube to increase during said trace intervals, and means .for controlling said low-mu tube to cause-its output' current to decrease during said trace inter' vals, said two control means being relatively pro.- portloned to regulate the output voltage across said low-mu tube during'sald trace intervals so that the rate of change of said saw-tooth current in said load circuit is maintained substantially uniform during said trace intervals.

14. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes effectively coupled across said load circuit with a given polarlty, a low-mu vacuum tube having output electrodes eii'ectively coupled across said load circuit with opposite polarity and having a control electrode, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and means for applying'to said control electrode a saw-tooth voltage derived from said load circuit of such polarity as to cause the output current or said low-.mu tube to decrease during said trace intervals and of such magnitude that the rate of change of said sawtooth current in said load circuit is maintained substantially uniform duringv said trace intervals.

15. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a rst vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a second vacuum tube having anode and cathode output electrodes effectively coupled across said load circuit with oppositepolarity and having a control electrode, means for controlling said first tube to cause its output current to increase durv ing said trace intervals, a coupling path from said anode to said control electrode for maintaining the anode-cathode resistance of said second tube less than its actual anode-cathode resist'- ance during said trace intervals, and means included in said coupling path for deriving a sawtooth voltage from said load circuit and for apcomprising a resistor effectively coupled between said cathode and said control electrode and a condenser effectively connected insaid coupling path between said anode and said control electrode for developing a saw-tooth voltage across said condenser and applying said saw-tooth voltage to said control electrode with such polarity as to cause the output current of said second tube to decrease during s ald trace intervals and with such magnitude that the rate of change of said saw-tooth current in said load circuit is held substantially constant during said trace intervals.

18. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said load circuit With opposite polarity, capacitance effectively coupled across said load circuit, means for controlling said high-mu tube to cutoi the output current of said high-mu 4tube during said y retrace intervals and to cause its output curplying said saw-tooth voltage between said anode and said control electrode with such polarity as to cause the output current of said second tube to decrease during said trace intervals and with such magnitude that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

16. A periodic Wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having output electrodes eiectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said load circuit with opposite polarity and having a control electrode, means for controlling said high-mu tube to cause its output current to increase during said trace intervals, and a series-connected resistor and condenser coupled to said load circuit, the saw-tooth voltage across said condenser being coupled to said control electrode with such polarity as to cause the output current of said lowmu tube to decrease during said trace intervals and with such magnitude that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

17. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linearl trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a rst vacuum tube having output electrodes effectively coupled across -said load circuit with a given polarity, a second vacuum tube having anode and cathode output electrodes eiectively coupled across said load circuit with opposite polarity and having a control electrode, means for controlling said first tube to cause its output' current to increase during said trace intervals, a coupling path from said anode to said control electrode, and means rent to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two last-mentioned means being relatively proportioned to regulate the output voltage across said low-mu tube during saidI trace intervals so that the rate of change of said sawtooth current in said load circuit is held substantiallyy uniform during said trace intervals.

19. A periodic wave generator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a highmu vacuum tube having input electrodes and having output electrodes eiectively coupled across said load circuit. with a given polarity, a low-mu vacuum tube having output electrodes effectively coupledacross said load circuit with `opposite polarity, capacitance coupled across said load circuit, control means for applying to said input electrodes a saw-tooth voltage of suchA polarity as to cause the output current' of said high-mu tube to increase during said trace intervals and a pulse voltage of such polarity as to out off said output current during said retrace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two control means being relatively proportioned to regulate the out-` put voltage across said low-mu tube during said trace intervals so that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

20. An oscillator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes coupled effectively across said load circuit withopposite polarity, means for controlling said high-mu tube comprising a feed-back circuit from said output electrodes to said input electrodes thereof for causing the output current of said high-mu tube to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two control means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals. l

21. An oscillator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with opposite polarity, means for coupling a saw-tooth feed-back voltage from the output electrodes to the input electrodes of said high-mu tube for causing the output current thereof to increase during said trace intervals, and means for coupling a saw-tooth feed-back voltage from the output electrodes to the input electrodes of said low-mu tube for causing the output current thereof to decrease during said trace intervals.

trace intervals comprising, a load circuit 'constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with opposite polarity, a capacitance coupled across said load circuit, means for coupling a saw-tooth plus pulse feed-back voltage from said output electrodes to said input electrodes of said high-mu tube for causing the output current thereof to increase during said trace intervals and to be eut off during said retrace intervals, and means for coupling a sawtooth feed-back voltage from said output to said input electrodes of said low-mu tube for causing the output current thereof to decrease during said trace intervals.

23. An oscillator for supplying to an inductive load circuit a. current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constitutingprimarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with opposite polarity, means for coupling a sawtooth feed-back voltage from said input to said output electrodes of said high-mu tube for causing the output current thereof to increase during said trace intervals, and means for controlling said load circuit is held substantially uniformduring said trace intervals.

24. .An oscillator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load vcircuit with a given polarity, a low-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with opposite polarity, capacitance coupled across said load circuit, means for coupling a saw-tooth plus pulse feed-back voltage from said output to said input electrodes of said high-mu tube for causing the voutput current thereof to increase during said trace intervals vand to be cut oil during said retrace intervals,

and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two last-mentioned means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

25. An oscillator for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu vacuum tube having output electrodes effectively coupled across said load circuit with opposite polarity, means comprising a capacitance and resistance coupled across said output 'electrodes of said high-mu tube for deriving a saw-tooth voltage, means for coupling said saw-tooth voltage to said input electrodes for causing the output current of said high-mu tube to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current'tor decrease during said trace intervals, said two lastmentioned means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate 0f change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

26. An oscillator for `supplying to an inductive load circuit a current of saw-tooth wave forin having relatively -long linear trace and short retrace intervals comprising, a load circuit constituting primarily inductance, a high-mu screengrid vacuum tube having input electrodes and having output electrodes effectively coupled across said load circuit with a given polarity, a low-mu triode vacuum tube having output electrodes effectively coupled across said load circuit with opposite polarity, and an inductive feedback means coupled from said load circuitgto said input electrodes for causing the output current of said high-mu tube to increase during said trace intervals, and means for controlling said low-mu tube to cause its output current to decrease during said trace intervals, said two last-mentioned means being relatively proportioned to regulate the output voltage across said low-mu tube during said trace intervals so that the rate of change of said saw-tooth current in said load circuit is held substantially uniform during said trace intervals.

27. A periodic wave repeater for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and short retrace intervals comprising, two vacuum tubes each having a cathode, an anode, and a control electrode, a space current supply-circuit for said tubes, said supply circuit and the anode-cathode circuits of said tubes being all connected in series in a closed direct current path, a load circuit constituting primarily inductance coupled eiectively in parallel with each of said tubes, a control-voltage circuit coupled to the control electrode of one of said tubes, and means for coupling to the control electrode-cathode circuit of the other of said tubes its anode-cathode voltage uctuations with the same polarity, whereby said other of said tubes is caused to present in series with said rst tube an effective anodecathode resistance less than its actual anodecathode resistance.

28. A periodic wave repeater for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and short retrace intervals comprising, two vacuum tubes each having a cathode, an anode, and a control electrode, a space current supply circuit for said tubes, said supply circuit and the anode-cathode circuits of said tubes being all connected in series in a closed direct current path, a load circuit constituting primarily inductance coupled effectively in parallel with each of said tubes, a control-voltage circuit coupled only to the control electrode of one of said tubes, a coupling path from the anode to the control electrode of the other of said tubes for coupling the anode-cathode voltage iluctuations thereof to the controlelectrode cathode circuit thereof with the same polarity so that said other tube is caused to present in series with said one tube an effective resistance less than its actual anode-cathode resistance.

29. A periodic wave repeater for supplying to an inductive load circuit a current of saw-tooth wave form having relatively long trace and short retrace intervals comprising, two vacuum tubes each having a cathode, an anode, and a control electrode, a space current supply circuit for said tubes, said supply circuit and the anode-cathode circuits of said tubes being all connected in series in a closed direct current path, a load circuit constituting primarily inductance coupled effectively in parallel with each of said tubes, a control-voltage circuit coupled only to the control electrode of one'of said tubes, and means including a coupling path from the anode to the control electrode of said other of said tubes for coupling to the control electrode-cathode circuit of said other of said tubes voltage uctuations of said load circuit with the same polarity as they appear across said load circuit, whereby said other of said tubes is caused to present in series with said first tube an eiective anode-cathode resistance less than its actual anode-cathode resistance.

30. A periodic wave repeater comprising, two vacuum tubes each having a cathode, an anode, and a control electrode, a space current supply circuit for said tubes, said supply circuit and the anode-cathode circuits of said tubes being connected all in series in a closed direct current path, a load circuit coupled eiectively in parallel with each of said tubes, a source of control voltage coupled to the control electrode of one of said tubes, and means for coupling to the control electrode-cathode circuit of the other of said tubes its anode-cathode voltage fluctuations with the same polarity, whereby said second tube is caused to present in series with said rst tube an effective resistance less than its actual anodecathode resistance.

HAROLD A. WHEELER. 

